Congestive heart failure (CHF) is most commonly associated with dilated left ventricle (LV) and/or its systolic dysfunction which is characterized by decreased ejection fraction (EF). In particular, a less 55% ejection fraction (EF) is the cut-off point for LV dysfunction (Wang T J, Levy D, Benjamin E J, Vasan R S. The Epidemiology of “Asymptomatic” left ventricular systolic dysfunction: Implications for screening. Ann Intern Med 2003; 138:907-913).
Regardless of its etiology, asymptomatic left ventricular systolic dysfunction (ALVSD) is considered an independent clinical entity as long as it is asymptomatic. Because of its progressive nature, when the ejection fraction (EF) declines below the 40% level, clinical signs, particularly of CHF, enable diagnosis and therapy. Hence it is the covert phase of 55%>EF>40% which remains undiagnosed, and which is prone to deteriorate either into an advanced stage of CHF, or to sudden cardiac death. On the one hand, CHF is considered one of the greatest medical economic burdens in the Western world, and early detection with the appropriate relative medical therapy would significantly improve the outlook of these patients. On the other hand, the largest population of patients with the ALVSD condition consists of individuals who have unrecognized coronary heart disease (CHD), including hibernating myocardium. The annual mortality, for example, of fatal arrhythmias in untreated hibernating myocardium is 16% (Allman K C, Shaw L J, Hachamovitch R, Udelson J E. “Myocardial viability testing and impact of revascularization on prognosis in patients with coronary artery disease and left ventricular dysfunction: a meta-analysis.”, J Am Coll Cardiol 2002; 39:1151-1158).
As the incidence of ALVSD in the community ranges from 3-7.7% (Wang T J, Evans J C, Benjamin E J, Levy D, LeRoy E C, Vasan R S., “Natural history of asymptomatic left-ventricular systolic dysfunction in the community”, Circulation 2003; 108:977-982), the only effective way to reduce the risks of ALVSD would be by diagnostic screening of the community (Wang T J, Levy D, Benjamin E J, Vasan R S., “The Epidemiology of “Asymptomatic” left ventricular systolic dysfunction: Implications for screening”, Ann Intern Med 2003; 138:907-913).
Techniques for non-invasive measuring and monitoring various hemodynamic parameters of a patient, such as cardiac parameters, utilizing body bioimpedance techniques have been developed. Some of such techniques are disclosed for example in the following patent publications: WO 02/078539, WO 97/24984, U.S. Pat. Nos. 5,469,859, 5,735,284, all assigned to the assignee of the present application.